The storing of agronomic crops such as potato tubers safely and efficiently has been a longstanding need in the agriculture industry. Many efforts have been made to maximize the time period of storage and to extend the useful life of the stored crop such that it retains its commercial utility and appeal. Generally, this storage involves tightly controlled conditions, such as ventilation, temperature, humidity and light.
Potato tubers, upon harvesting, are in a dormant state and are stored in storage facilities as described for example, in U.S. Pat. No. 4,226,179 to Sheldon III, and U.S. Pat. No. 4,887,525 to Morgan. These storage facilities typically provide controlled ventilation and protection from light to large piles of potatoes, which are typically on the order of 16 feet to 20 feet high, and as large as 130 feet wide by 400 feet in length.
Potatoes are often stored for appreciable periods, resulting in sprouting. The problem of sprouting is extensive, and can result in a diminution in the economic value and edibility of the stored potatoes. In efforts to prevent sprouting, potatoes are frequently stored at cool temperatures, e.g., about 40 degrees F. Although storage at cool temperatures does minimize sprouting, it causes dark color and flavor changes in fried potato products. Higher storage temperatures, as high as 52 degrees F. and above, are used to get good fry color. The higher storage temperatures needed to get good light fry color promote sprouting.
In an effort to control sprouting at the higher storage temperatures needed to get good fry color, chemicals such as isopropyl-N-(3-chlorophenyl) carbamate also known as “CIPC” have also been utilized by the potato industry. CIPC is the most important sprout inhibitor utilized in the commercial storage of potatoes, and is especially critical for potatoes used in the manufacture of French fries and potato chips, as consumers desire these products to have a light fry color and good flavor.
CIPC inhibits sprouting by inhibiting cell division. In order for CIPC to be beneficial, every potato eye must be treated. Thus in order to successfully apply CIPC in the large potato piles of the storage facility, CIPC is typically in the form of an aerosol of fine particles that scatter visible light and are therefore visible to the eye as a smoke or fog and which allow the aerosol to be evenly distributed to the potatoes utilizing diffusion.
In order to generate an aerosol or fog of CIPC, thermal aerosol generators are typically used as shown in FIG. 1A. These thermal generators utilize air taken from outside the storage facility, which is then heated to a high enough temperature to vaporize a suitable CIPC formulation, for example melted solid CIPC or a CIPC solvent solution. Typically, the CIPC vapor/air mixture has an exhaust temperature anywhere from about 700 degrees F. to about 850 degrees F. When the hot CIPC vapor/air mixture is introduced into the much cooler storage facility, a fog or aerosol of CIPC is formed.
A major disadvantage to the use of these thermal foggers is that they heat the CIPC formulation to very high temperatures, which can be a fire hazard. The autoignition temperature of CIPC and its typical formulations is about 734 degrees F. Thus, under the normal operating conditions of a thermal fogger machine, the CIPC vapor air mixture exiting the machine is typically about 800 degrees F., well above the autoignition temperature of CIPC. If the concentration of the CIPC or mixture with other combustibles exceeds its lower flammable limit, the CIPC or its mixture can ignite and burn. Another disadvantage is that the temperature of the CIPC vapor mixture greatly exceeds the autoignition temperature of ordinary combustibles such as for example, paper and wood. Possibly the single greatest threat of fire to a potato storage facility is caused by the autoignition of ordinary combustibles.
Another disadvantage to prior art systems such as shown in FIG. 1A is that outside air is used by the thermal aerosol generator and introduced with the CIPC into the storage system. Thus, in order to maintain a mass balance within the storage system, air and consequently CIPC must be vented from the storage system. As a result, CIPC is exhausted into the environment and thus contributes to pollution, as well as reducing the overall system efficiency. The system inefficiency is also referred to as a displacement loss.
Thus, an improved method and apparatus is desired for generating an aerosol of sprout inhibitors which has a reduced incidence of fire and the improved system efficiency.